Automatic farming apparatus

ABSTRACT

AUTOMATIC FARMING APPARATUS FOR USE IN FARMING A FIELD WHEREIN A TRACOT PULLING A FARMING IMPLEMENT SUCH AS A PLOW IS ADAPTED TO TRACE A PATH DEFINED BY A PLURALITY OF MAIN TRACING LINES. A PAIR OF SECONDARY TRACING LINES ARE BURIED OUTSIDE THE EDGES OF THE FIELD, AND MEANS ARE PROVIDED FOR CAUSING THE TRACOR TO LEAVE A MAIN TRACING LINE AT THE END OF EACH ROW, AND AUTOMATICALLY MOVE OVER TO THE ADJACENT SECONDARY TRACING LINE WHICH IT TRACES UNTIL IT IS TURNED TOWARD ANOTHER MAIN TRACING LINE. THE TURNING OPERATION BETWEEN THE MAIN AND SECONDARY TRACING LINES IS CONTROLLED AS A FUNCTION OF THE DISTANCE TRAVELLED BY THE TRACTOR. THE MAIN TRACING LINES COMPRISE A PLURALITY OF PARALLEL CONNECTED WIRES EXTENDING FROM EDGE TO EDGE ACROSS THE FIELD. AN ADDITIONAL PAIR OF CONTROL LINES ARE BURIED AT RESPECTIVE EDGES OF THE FIELD TO CONTROL THE OVERALL SEQUENCE OF THE VEHICLE TURN SEQUENCE.

Sept. 21, K, usmfl ETAL I AUTOMATIC FARMING APPARATUS Original FiledApril 5.. 1967 *3 Sheets-Sheet 1 FIG. 3

INVENTORS KARL RUSHING JOHN CLARENCE ALLEN JR.

ATTORNEYS Sept? 21,1971 -K. Rusumg A AUTOMATIC FARMING APPARATUSOriginaLFiled April 5. 1967 FIG. 38

R PR 3 Sheets-Sheet I PHASE DETECTOR STEERING MOTOR CCW INVENTORS KARLRUSHING JOHN CLARENCE ALLEN JR.

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ATTORNEYS Sept. 21, 1971 RUSHlNG ETAL AUTOMATIC FARMING APPARATUS IOriginal Filed April 5, 1967 3' Sheets-Sheet 3 8 ,7 5 a oo 55;

Z 5:3 J 8 2: Nm uwim U m3 -1 =6 52. wzEnmFm mm INVENTORS KARL RUSHINGJOHN CLARENCE ALLEN JR.

BY K

ATTORNEYS United States Patent 3,606,933 AUTOMATIC FARMING APPARATUSKarl Rushing, Indianola, Miss., and John Clarence Allen,

Jr., P.0. Box 87, Indianola, Miss.; said Rushing assignor to said Allenand Roy Rodgers Brashier Application Apr. 5, 1967, Ser. No. 628,616, nowPatent No. 3,468,391, dated Sept. 23, 1969, which is acontinuation-in-part of application Ser. No. 531,603, Mar. 3, 1966, nowPatent No. 3,468,379. Divided and this application Oct. 31, 1968, Ser.No. 772,256

Int. Cl. B62d /04 US. Cl. 180-98 5 Claims ABSTRACT OF THE DISCLOSUREAutomatic farming apparatus for use in farming a field wherein a tractorpulling a farming implement such as a plow is adapted to trace a pathdefined by a plurality of main tracing lines. A pair of secondarytracing lines are buried outside the edges of the field, and means areprovided for causing the tractor to leave a main tracing line at the endof each row, and automatically move over to the adjacent secondarytracing line which it traces until it is turned toward another maintracing line. The turning operation between the main and secondarytracing lines is controlled as a function of the distance travelled bythe tractor. The main tracing lines comprise a plurality of parallelconnected wires extending from edge to edge across the field. Anadditional pair of control lines are buried at respective edges of thefield to control the overall sequence of the vehicle turn sequence.

This is a division of US. patent application Ser. No. 628,616, filedApr. 5, 1967 (now Pat. No. 3,468,391) which is a continuation-in-part ofUS. patent application Ser. No. 531,603, filed Mar. 3, 1966 (now Pat.No. 3,468,- 379).

The above mentioned application No. 531,603 relates to an automaticfarming system wherein a tractor is caused to follow a path defined by amain tracing line buried in the field to be farmed. The system disclosedin Patent No. 3,468,379 is an improvement over automatic farmingapparatus such as disclosed in Us. Pats. Nos. 2,842,039 and 3,169,598.The present invention is designed for use in such a system and, incertain respects is an improvement over the overall system. Morespecifically, this invention relates to a configuration of buriedconductors, including the main tracing lines and two pairs of additionallines used to control the tractor operation when itis turned from onetracing line to the next successive one. The in vention further relatesto the means by which such tractor operation is controlled.

Briefly, in accordance with the invention, a plurality of main tracinglines, running edge to edge across the field to be farmed, are buried,with two edge conductors gerierally transverse thereto being buriedalong each edge of the field. When the tractor senses the first of theedge conductors an automatic turn sequence is initiated which causes thetractor to move from the first conductor toward the outer edgeconductor. The tractor picks up this outer edge conductor and traces thepath defined by it for a predetermined distance. The tractor is thencaused to turn back toward the field and into proximity to a second oneof the main tracing wires which it picks up and follows to the otheredge of the field. At such other edge, substantially the same turnsequence (but in the other direction) is initiated to move the tractorover the next area of the field to be farmed. In the preferredenvironment, the main tracing wires comprise a plurality of parallelwires which are electrically connected in parallel to source ofalternating voltage at a first frequency.

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In the drawings:

FIG. 1 is a schematic illustration of a preferred embodiment of theinvention;

FIG. 2 is a top view of a tractor modified in accordance with theinvention;

FIG. 3A is a detailed view of the signal receiving means according tothe invention;

FIG. 3B is a block diagram of a steering control circuit for use withthe tractor of FIG. 2;

FIG. 4 is a schematic diagram showing how the invention causes a vehicleto trace a path defined by a conductor; and

FIG. 5 is a block diagram of a circuit which may be used with theinvention for automatic farming purposes.

FIG. 1 illustrates schematically the wires as they would actually beplaced on a representative tract of land. The tractor or other vehicleis shown generally at 10' pulling a farm implement 12 such as a plow.Obviously, the various parts are not drawn to scale. A tracing circuit14 is buried throughout the length of the field so as to form parallelrows of buried main tracing lines shown as wires 14a, 14b, 140, etc.,all of which are electrically connected in shunt. The wires 14 areburied a sufficient distance beneath the surface so as not to bedisturbed by implement 12, for example, about two feet.

Tractor 10 carries a signal receiving means 16 mounted on a boom 18extending from the front of tractor 10. As explained in detail below,receiver 16 picks up signals from one of the tracing Wires 14 (14b inthe illustrated case) which are used to maintain the tractor in a fixedposition with respect to the tracing wire. Thus, tractor 10 will travelalong the path indicated by dotted line 20 while pulling implement 12through the field.

A pair of control lines 22a and 22b are buried at opposite edges of thefield so that each crosses the main tracing lines 14a, 1412, etc. A pairof secondary tracing lines 24a and 24b, substantially parallel tocontrol lines 22a and 22b, respectively, are buried in the fieldslightly beyond and parallel the respective control lines 22a and 22b.As shown, the control lines 22 and secondary tracing lines 24 aresubstantially transverse to the main tracing lines 14.

A conventional signal generator 14' applies an alternating voltage of afirst frequency to the parallel main tracing lines 14a, 14b, etc., and asimilar signal generator 22 similarly energizes the control lines 22a,22b and secondary tracing lines 24a and 24b, all of which are con nectedin shunt with respect to generator 22'. The tractor also includes asecond and third signal receiving means 25 and 26, respectively, forreceiving the alternating signal impressed on control lines 22 andsecondary tracing lines 24, respectively. In the preferred embodiment,receivers 25 and 26 are identical to receiver 16. The signals on lines14, 22 and 24 are used for the control of tractor 10 and implement 12,as explained below. The following description with respect to FIG. 1 isgiven in purely functional terms for explanatory purposes.

As tractor 10 proceeds along path 20 with receiver 16 over tracing line14b, various steering servos maintain the tractor 10 in its properlyaligned position so that implement 12 cuts a straight path across thefield. When receiver 25 picks up the tone on control line 22a (whichdiffers from the tone on tracing line 14) it causes a programmed turnsequence to be initiated depending upon the edge of the field which thetractor is approaching. In other words, if tractor 10 is travelling frombottom to top in FIG. 1, the signal on control line 22a, when received,would override the signal on tracing line 14 and cause the tractor tocommence a ninety degree right turn as shown by the dotted line portion20a. Prior to the turning operation the signal on control line 22acauses a mechanism (not illustrated) to reduce the vehicle speed andlift the implement 12 out of the ground which, for

known reasons, is desirable when the tractor is turning.

After the turn is commenced, receiver 26 causes the tractor to seek thesecondary tracing line 24a and follow that line as shown at 20b. After apredetermined delay or distance, which, as explained below, may readilybe incor'porated into the preferred embodiment of the invention, thecontrol apparatus on the tractor causes the tractor to commence aninety-degree turn back toward the field along the path 20c. The tractorthen commences to seek main tracing line 14a. In other words, the signalfrom receiver 16 responsive to main tracing line 14 causes the tractorto move on a path 20d toward the main tracing line closest to it, which,in this example, is line 14d.

The tractor follows line 14d along path 202 until the signal on line 22bis received. At this point substantially the same operation as describedabove recurs with the initial programmed turn being to the left. Tractor10 continues along the path defined by secondary tracing line 24b for apredetermined interval of time and then turns to the left to seek andfollow main tracing line Me.

This procedure continues until the entire area has been covered.Depending upon the number of tractors, the width of the implement, etc.,more than one pass over the area may be required, but this presents nospecial problems, and representative tracing patterns are given inapplication No. 531,603 with reference to FIG. 4 thereof.

The preferred configuration of the buried conductors differs from thatshown in application No. 531,603 in that the main tracing lines 14 areelectrically connected in parallel and a single frequency is applied tothe control line 22 and secondary tracing line 24. This parallelarrangement of the main tracing lines avoids problems which arose with aserpentine (or serial) configuration due to the inducing of out-of-phasevoltages into adjacent tracing lines. The use of a single frequency forlines 22 and 24 is preferred primarily from the viewpoints of simplicityand economy.

FIG. 2 is a detailed view of the essential elements of the tractorconstruction insofar as they relate to the present invention. Signalreceiving means 16 is mounted on a bar 28 pivotally pinned to the arm 18at 29. Similarly, the receiver 26 is mounted directly on a rod 30 whichis pivotally pinned to arm 18 at 31. The position of the individualreceivers with respect to rods 28 and 30, and the distance between thetwo may be made adjustable by obvious means (not illustrated). It is notalways necessary to mount receiver 16 on a boom, and in certainapplications it may be desirable to position receiver 16 on rod 30, orits equivalent, as shown in dotted lines.

The front wheels 32 of the tractor are mechanically linked in anysuitable fashion to a central lever 34 pivotally mounted, for example,on the tractor frame (not shown), so that lever 34 pivots when thewheels 32 are turned in either direction. A third bar 36 is pinned tothe arm 18 at 37 and linked to lever 34 by push-pull control cable 38passing over guide rollers 40 and 42 which are mounted on the tractor 10and arm 18, respectively. The cable link 44 connects the free end of therod 28 to rod 36 and a similar push-pull control cable 46 mechanicallycouples the rod 36 to the bar 30 on which receiving means 26 is mounted.The purpose of this construction is to ensure that the receivers arealways oriented in the same direction as the front wheels. Obviously,any suitable means for achieving this objective may be substituted forthe construction illustrated in FIG. 2.

The mechanical constructions of receivers 16 and 26 are identical andtherefore only receiver 16 is explained in detail. As shown in FIG. 3A,receiving means 16 con sists of three sections, 16A, 16B and 16C. Eachsection comprises a coil 16a, b or c wound about a respective ferritecore, 16a, b, or c, the electrical connections of which are illustratedand described with reference to FIG. 3B. Physically, the axes of thecoils 16a, 16b and are aligned as illustrated in FIG. 3A, that is, withcoil 16a perpendicular to the direction in which front wheels 32 arefacing, and with coils 16b and 160 each at an angle of 60 with respectto such direction. As will become more apparent below, this angle is notcritical but has been selected as a value which provides optimum resultsin a particular practical embodiment. Each coil comprises a separatesignal detector, which, as known, has maximum effectiveness (i.e.receiving ability) for signals arriving from the direction along whichits axis is aligned. In other words, when a coil such as 16a isperpendicular to the conductor 14, its voltage output is a maximum for agiven distance between the coil and conductor.

FIG. 3B is a semi-schematic electrical diagram showing the manner inwhich the coils of the antennas 16 and 26 are interconnected withrespect to the steering circuits for the tractor. The coils 16b and 160are of equal inductance and connected so that opposing voltages areinduced in the respective coils. The capacitor 50 is shunted across theseries connection of coils 16b and 16c to form a circuit which isresonant at the frequency of generator 14', for example, 14,000 Hz.Coils 26b and 26c are also equal and connected in a series-opposingrelation with a capacitor 52 connected across the combination toresonate the circuit at the frequency of generator 22, for example, 2800Hz. With this arrangement, receiver 16 only responds to the signals onmain tracing line 14 and receiver 26 to the signals on lines 22 and 24.A capacitor 54 is connected directly across the third coil 16a andcapacitor 56 across coil 26a to resonate these coils at the frequenciesof generators 14 and 22, respectively.

The initiation of the various circuit operations are controlled by therelay illustrated and described with reference to FIG. 5. In FIG. 3B,two contacts a1 and 02 of one such relay are shown in their positionwhen receiver 16 is guiding the tractor.

With relay contacts a1 and a2 in the condition illustrated, thedifference between the voltage induced in coils 16b and 160 is amplifiedby an amplifier 58 and coupled to a phase detector 60 which comparesthis difference voltage with the reference voltage induced in coil 16aand amplified by amplifier 62. Phase detector 60 is a conventionaldevice which, for example, produces a binary 1 or enable signal on anoutput line 64 and a binary 0 or inhibit signal on another output line65 when the outputs of amplifiers 58 and 62 are in phase. When theoutput of amplifier 58 is out-of-phase with the output of amplifier 62,the output condition of detector 60 reverses, i.e., a binary 1 appearson line 65 and a binary 0 on line .64. This indicates which of the coils16b or 160 is receiving the stronger signal, since, assuming coils 16aand 16b are wound to produce in-phase voltages, if the voltage inducedin coil 16b is greater than the voltage induced in coil 160, the inputsto detector 60 will be in phase. On the other hand, if the voltageinduced in coil 16c is greater than that induced in coil 16b, thevoltage output of amplifier 58 will be 180 out of phase with thereference voltage across coil 16a.

If an enable output appears on line .64, it is passed through an ANDgate 66 and an OR gate 68 to the steering motor 70, causing the outputshaft 72 of the motor to rotate, for example, in a clockwise direction.If an enable output appears on line 65, it is coupled through an ANDgate 74 and an OR gate 76 to the motor 70 to cause output shaft 72 torotate counterclockwise. Of course, when gate 66 is opened, gate 74 isinhibited by the output of detector 60 and vice versa. If the voltagesinduced in the coils 16b and 160 are identical, there is no output fromamplifier 58, in which case phase detector 60 applies a binary 0" orinhibit signal to both lines 64 and 65, which will have no effect uponmotor 70. This is the condition which exists when the tractor is tracingproperly with respect to the tracing wire 14. By way of example, phasedetector 60 may be a conventional ring modulator, in which case it maybe desirable for AND gates 66 and 74 to include DC amplifiers to providesufficient power to switch the controls for the motor 70. As explainedbelow, gates 66 and 74 are normally enabled by the absence of signals onthe inhibit inputs labelled RR and RL, respectively.

FIG. 4 is an explanatory diagram showing how the automatic controlcircuit of FIG. 3B achieves the desired function. Tractor is shown infive positions, labelled position I to position V, on a typical pathapproaching a tracing wire 14. In position I, coil 160 is substantiallyperpendicular to the wire 14, while the coil 16b is almost parallelthereto. Accordingly, the signal induced in coil 16c is substantiallystronger than that induced in coil 16b and steering motor 70 is causedto turn the wheels 32 of the tractor to the right. Since wheels 32 aremechanically linked to the antenna 16 (see FIG. 2) the tractor willassume the condition shown in position II of FIG. 4. In this condition,coils 16b and 160 are at virtually the same angle with respect to line14, but coil 16b is substantially closer to the line than is coil 160.Accordingly, in position II, the voltage induced in coil 160 is greaterthan the voltage induced in coil '16!) and phase detector 60 switchesthe binary 1 or enable signal from line .64 to line 65, causing thesteering motor 70 to operate so as to turn the wheels toward the left.This new condition is illustrated in position III and, since coil 16b isstill closer to the line 14, it still receives the stronger signal andcontinues to operate the motor 70 to turn the wheels 32 to the left.

As the wheels start to the left from position III, coil 16c becomessubstantially perpendicular to the line 14 and therefore receives thestronger signal, thus causing the tractor to start turning to the rightas shown in position IV. This hunting continues until the tractorreaches the position shown in position V where the outputs of coils 16band 16c are completely balanced so that the tractor will trace along thedesired path. If there is any deviation of the tractor 10 with respectto the tracing line 14, the operation to realign the two issubstantially as described.

This particular arrangement whereby the signal receiving means isresponsive not only to proximity to the tracing line, but also theorientation of the receiver with respect to the line, enables veryaccurate tracing with relatively inexpensive electronic circuits andwithout the need for accurately measuring the difference between variousanalog signals, as is customarily the case in automatic tracing circuitsof this nature. In the preferred embodiment, audio frequencies areemployed and the receiving means couple directly into the near field ofthe conductor. conceivably, the principles of the invention may also beapplied with directional radio frequency antennas in place of the coils.

The said application No. 531,603 discloses specific means forautomatically programming the tractor and farming implements as well asthe remote control radio system. It is contemplated that the features ofthe present invention may be used in the identical system, however, suchfeatures are not restricted to a particular environment or even tofarming purposes.

The programming device in said application No. 531,603 is primarily anelectronic system. It has been found, that for farming purposes, a verysimple electromechanical system using stepping relays and relay logiccircuits can accomplish all that is required of the program unit whilesubstantially reducing expense and increasing reliability. A blockdiagram of such an electromechanical program unit is illustrated in FIG.5.

Referring to FIG. 5, when the tractor 10 passes over the control line22a or 22b (see FIG. 1), a signal is detected by signal receiving means25 located beneath the tractor (the same signal is also picked up byreceiver 26, but this latter receiver is disconnected by virtue of therelay contacts a1 and a2; see FIG. 3B). The output of receiver 25 isamplified by an amplifier the output of which in turn enables an ANDgate 82 and sets a switch 84 as explained below. Receiver 25 does notcontrol the actual tracing operation and may therefore comprise a singlecoil tuned to the frequency applied to control lines 22a, b. In anoperable embodiment of the invention, however, receiver 25 was of thesame construction as receivers 16 and 26 to provide a more precise andreliable wire crossing indication.

Tractor 10 may have a small microswitch 8 6 physically positionedadjacent an axle of the tractor and adapted to be actuated byappropriate cams secured to the axle during rotation thereof. By way ofexample, the microswitch 86 may be actuated twice during each fullrevolution of the front wheels so that two equally spaced pulses willappear on line 87 each full revolution of the front wheels. As a typicalexample, such pulses may occur every four feet traversed by the tractor.

The pulses on line 87 pass through the AND gate 82 after it has beenenabled by a signal from receiver 25 to energize a stepping relay 90.Stepping relay 90 is a conventional relay which may energize one or moreof a plurality of output lines depending upon the number of input pulsesreceived through the AND gate 82. The stepping relay may include aplurality of rotary switches connected in parallel so that the relayoutput is in effect a binary count corresponding to the number of inputpulses received. Conceivably, the stepping relay 90 may energize one ormore of a plurality of outputs by means of a single rotary switch so asto similarly initiate the required operation.

The first operation to occur after crossing control line 22a is to raisethe farming implement from the ground; therefore, the first output ofstepping relay 90 is a signal on line 91 which causes an implementraising means 92 to lift the implement. Immediately thereafter, a signalis applied to the line 93 by relay 90 to cause a device 94 to throttledown the tractor so that the tractor speed is substantially reduced forthe programmed turn operation.

The programmed turn is initiated by a signal PR or PL from the switch 84depending upon its state. For example, referring to FIG. 1, if tractor10 is travelling from bottom to top it is desired to turn the tractor tothe right after crossing line 22a, switch 84 is set so that upon receiptof a signal from amplifier 80, a signal is applied to the line PR. Thissignal is then coupled through the OR gate 68 (FIG. 3B) to the steeringmotor 70 such that the output shaft 72 rotates to turn tractor 10 to theright. At the same time, the signal on line 95 energizes the relay Awhich operates the contacts a1 and a2 (FIG. 3B) such that the receiver26 is coupled into the steering motor control circuit. The signal PRwill only last for a short period of time, after which the tractor iscontrolled by the signals detected by coils 26b and 26c in the samefashion as previously described with respect to coils 16b and 160. Ofcourse, when under the control of receiver 26, tracing occurs along theline 24a or 24b rather than one of the lines 14.

After the tractor has travelled a predetermined distance, a secondsignal is applied to the line 95 and passed through switch 84 to theoutput line PR causing a second right turn to be initiated. This secondright turn corresponds to the tractor path 200 illustrated in FIG. 1 andwill direct the tractor back toward one of the wires 14. After thissecond right turn is commenced, the stepping relay 90 applies a signalto line 97 which energizes an implement control means 98 to lower thefarming implement into the earth. A second signal on a line 99 from thestepping relay 90 causes a further control device 100 to increase thespeed of the tractor to its normal rate. The appearance of the secondpulse on line 95 also de-energizes relay A so that the contacts a1 anda2 illustrated in FIG. 3B are returned to the illustrated condition,i.e. with the tractor under the control of signal from receiver 16. Thetractor will then continue to trace along one of the lines 14 until suchtime as the wire 22b is crossed at the far end of the field.

To cause the required alternate right and left turning sequence atopposite ends of the field, switch 84 may be a bi-stable device whichchanges condition upon receipt of successive pulses from amplifier 80whereby the lines PR and PL are alternately energized. Thus, when theline 22b is crossed, switch 84 will be switched to its second statecausing the out-put line PL to initiate a program left turn sequencealthough the implement raising and lowering operations as well as thethrottling operations will be the same as that described above.

The description of FIG. has been given in block diagram terms sincethere are innumerable different ways in which the programmed sequence ofoperations can be controlled. As described, all of the requiredoperations may occur within a predetermined distance after the firstcrossing of one of thelines 22a or 22b, or within a fixed time intervalof such crossing. Similarly, the operations may occur at or about thetime the tractor crosses the line 22a or 22b, that is signals from thereceiver 25 may directly control the implement and throttling operationsof the tractor.

As explained in application No. 531,603, the invention is not limited tospecific means for raising and lowering the. implement or for changingthe speed of the tractor, and the references incorporated therein applyequally to the present invention. To avoid redundancy, thepresentdisclosure contains no specific reference to the remote radio controlcircuits, but again the systems illustrated in application No. 531,603can be used for that purpose. In FIG. 3B, the lines labelled RR and RLrepresent, respectively, remote right and remote left operationsinitiated by means of a radio signal. The presence of either of thesesignals will override any of the programmed or automatic signalsappearing in the circuit.

What is claimed is:

1. For use with automatically controlled farming apparatus wherein afarming vehicle is adapted to trace a path defined by a configuration ofburied wires, a wire configuration comprising,

a. plurality of generally parallel main tracing lines runningsubstantially from edge to edge across said field, said main tracinglines being connected in parallel,

a pair of control lines generally defining the respective edges of saidfield,

a pair of secondary tracing lines lying outside the respective edges ofsaid field for guiding said vehicle from one of said main tracing linesto another of said main tracing lines,

first means for generating an alternating voltage of a first frequencyconnected to said main tracing lines, and

second means for generating an alternating voltage of a second frequencyconnected to said control lines and secondary tracing lines.

2. A wire configuration according to claim 1, wherein said control linesand secondary lines are connected in parallel across said secondgenerating means.

3. For use with automatically controlled farming apparatus wherein afarming vehicle including a farming implement is adapted to trace a pathdefined by a configuration of buried wires, said vehicle including meansfor sensing the presence of said buried wires, and means responsive tosaid sensing means for steering said vehicle along a path defined bysaid buried wire, the combination of a buried wire configuration andvehicle control means, said Wire configuration comprising a plurality ofgenerally parallel main tracing lines running substantially from edge toedge across said field, said main tracing lines being connected inparallel,

a pair of control lines generally defining the respective edges of saidfield, and a pair of secondary tracing lines lying outside of therespective edges of said field forguiding said vehicle from one of saidmain tracing lines to another of said main tracing lines, said vehiclecontrol means, comprising means responsive to detection of one of saidcontrol lines by said sensing means for causing said steering means toturn said vehicle in a first direction into the vicinity of one of saidsecondary tracing lines,

means for operating said steering means in response to said sensingmeans to steer said vehicle over a path defined by said one secondarytracing line, and

means for causing said steering means to turn said vehicle a second timein said first direction into the vicinity of said other one of said maintracing lines.

4. The combination according to claim 3, wherein said means for turningsaid vehicle a second time is operable after said vehicle has travelleda predetermined distance from said one control line.

5. The combination according to claim 3, including means for generatingan alternating voltage of a first frequency connected to said maintracing lines and means for generating an alternating voltage of asecond frequency connected to said second and thirdconductors.

References Cited UNITED STATES PATENTS 2,317,400 4/1943 Paulus et al.l79.l 2,842,039 7/1958 Swingle 172-3 3,169,598 2/ 1965 Finn-Kelcey etal. 180-79 3,294,178 12/1966 Lawson et al. l8079.lX 3,495,662 2/ 1970Welch 1723 KENNETH H. BETTS, Primary Examiner US. Cl. X.R..

